Thrash metal's "big four" – Metallica, Slayer, Megadeth and Anthrax – defined the genre in the 80s, putting out records of frightening pace, bruising power and lyrics that focused on alienation, death and fear. Their Friday night appearance at Knebworth as part of the touring Sonisphere festival, now in its third year, was their first appearance together in the UK and had a feeling of history about it, not least because the groups' heydays are mostly well in the past.

But if Megadeth felt dated, Slayer still had the vigour to take your breath away, tearing through Angel of Death as juddering riff followed screeching solo. Metallica know exactly how to rock a festival. Fittingly, their faster early material dominated as they prowled the stage like cats and flames rose into the night sky. They played tight and hard for two hours, making populist speeches about "the metal family" and wheeling the rest of the big four on stage for a crunching cover of Diamond Head's Am I Evil, a line of axemen fronting the stage as devil horns punched from the crowd.

Saturday felt less cohesive thanks to biblical downpours and a lineup that stretched from the potent Cavalera Conspiracy – who whipped up a mosh pit of merchandise T-shirts, a fancy-dress cow and a Brazilian flag – to Weezer's catchy power pop. Kilmarnock three-piece Biffy Clyro have become one of the UK's biggest cult bands largely because of their live act, and as night drew in they formed a swaggering blur of pale skin and tattoos. Their quieter numbers were cloying, but when they ramped it up, with epic choruses, tempo shifts and fierce shrieking, they felt elemental: headliner status suits them.